1. Field of the Invention
The present invention relates to a fuel injection device for an internal combustion engine having a fuel supply pump that controls a fuel amount discharged to fuel injection valves mounted for respective cylinders of the engine. Specifically, the present invention relates to a pressure accumulation fuel injection device having a supply pump that meters a fuel suction amount with an electromagnetic valve to control a fuel discharge amount pressure-fed to a common rail.
2. Description of Related Art
A common rail fuel injection system known as a fuel injection system for a diesel engine has a common rail for accumulating high-pressure fuel which is distributed to multiple injectors mounted for respective cylinders of the engine. The high-pressure fuel is injected and supplied into a combustion chamber of each cylinder of the engine from the injector of the cylinder at predetermined timing. The high-pressure fuel is pressure-fed from a fuel supply pump, which can vary a discharge amount, to the common rail. The pressure-feeding amount (fuel discharge amount) is feedback-controlled. As such a fuel supply pump, there is a suction amount metering supply pump that determines the fuel discharge amount when the fuel is suctioned (for example, as described in JP-A-2004-293540).
The supply pump has an electromagnetic valve that controls a fuel suction amount suctioned into a pressurization chamber. For example, the electromagnetic valve controls a position of an inner valve with drive current applied to a solenoid coil to change an opening area (valve opening degree) of a fuel suction passage leading from a feed pump to the pressurization chamber, regulating the fuel suction amount. Thus, the fuel supply pump controls a fuel discharge amount discharged from the pressurization chamber to the common rail.
It is known that drive current/fuel discharge characteristics contain a large individual difference for each supply pump as shown by broken lines in FIG. 5. A solid line in FIG. 5 represents a standard characteristic (pump instrumental error median product characteristic). It is known that the fuel discharge amount D in an idling operation period varies so that the fuel discharge amount D is offset along a direction of current (drive current) I from the standard characteristic as shown by an arrow mark in FIG. 5. Therefore, a conventional technology performs learning control for learning and correcting a variation in characteristics due to an instrumental error of the supply pump by calculating a deviation in the direction of current I (current learning value) with respect to the standard characteristic in the idling operation period in which various engine conditions are stabilized.
In the case where the learning control is performed for the first time when a vehicle is shipped from a factory (at vehicle factory shipment), as shown in a time chart of FIG. 6, tentative learning is performed only once when engine cooling water temperature is low at the vehicle factory shipment, and then, main learning is performed only once when engine warm-up is completed. Values 5, 1, 0, 2 of a learning mode shown in FIG. 6 represent an initial state (initial state at factory shipment, for example), a tentative learning completion state, a learning state, and a main learning completion state respectively. Values 2, 1 of a learning flag in FIG. 6 represent learning execution and learning inexecution, respectively. A sign ISTUDY represents the actual learning value and α is a theoretical learning value. In FIG. 6, a condition for the tentative learning is satisfied at time A and the tentative learning is performed during an interval “a.” A condition for the main learning is satisfied at time B and the main learning is performed during an interval “b.”
The tentative learning is just a temporary pump instrumental error learning method and is performed to absorb the variation in the characteristics due to the instrumental error of the fuel supply pump as early as possible. The variation of the characteristics due to the instrumental error of the fuel supply pump can be absorbed by performing the tentative learning when the engine cooing water temperature is low. However, accuracy of a tentative learning value obtained through the tentative learning is lower than the accuracy of the actual learning value obtained through the main learning. For example, if the tentative learning is performed only once when the engine cooling water temperature is low in the case where the main learning is performed when the engine cooling water temperature is in a predetermined range, the tentative learning value obtained through the tentative learning differs largely from the actual learning value obtained through the main learning. Accordingly, the main learning is invariably necessary after performing the tentative learning.
However, a commercial car having a large heat capacity (for example, a vehicle equipped with a six-cylinder direct injection turbocharger four-cycle diesel engine) requires a long period for completing the engine warm-up (for example, it takes about 8 minutes for the engine cooling water temperature to increase from ordinary temperature to 65° C.). Therefore, if the main learning is performed for the first time at the vehicle factory shipment, it takes a long time to complete the main learning, deteriorating productivity at the factory.
In order to achieve at the same time early absorption of the variation of the characteristics due to the instrumental error of the fuel supply pump and improvement of the factory productivity through shortening of the learning period at the vehicle factory shipment, the tentative learning may be performed at the vehicle factory shipment and the main learning may be performed in the market after the vehicle factory shipment. In this case, the variation of the characteristics due to the instrumental error of the fuel supply pump is not absorbed thoroughly because the accuracy of the tentative learning value obtained through the tentative learning is low. If the engine test is continued in such a state a deviation between target common rail pressure and actual common rail pressure is continuously generated. For example, if the deviation between the target common rail pressure and the actual common rail pressure is continuously generated in an OBD-II (On Board Diagnostic system stage II) control subject car obliged to monitor a vehicular exhaust emission control condition with an in-vehicle computer, there is a possibility that the computer of the OBD-II system determines that the exhaust emission is deteriorated and turns on a warning lamp such as MIL (malfunction indicator lamp, engine check lamp) on a factory shipment liner stopping the factory shipment line.